It is known that particles of fibrous basic magnesium sulfate [MgSO4.5Mg(OH)2.3H2O] are utilized as wastewater-processing material. This utilization is disclosed in the following published documents.
JP-A-6-226017 discloses a method for removing fine particles and oil from wastewater, by the use of basic magnesium sulfate granules comprising a plurality of fibrous basic magnesium sulfate particles. This document describes a method comprising the steps of bringing the basic magnesium sulfate granules into contact with wastewater containing fine particles and oil to aggregate the fine particles and oil on the granules, filtering the aggregated fine particles and floating the aggregated oil for separation.
JP-A-2005-231927 discloses basic magnesium sulfate granules comprising a plurality of fibrous basic magnesium sulfate particles bonded together with fibrous inorganic material such as xonotlite or sepiolite or fibrillated polytetrafluoroethylene. It is stated that the basic magnesium sulfate granules can well maintain their form in running water as compared with basic magnesium sulfate granules produced without employing a binder, and hence these are useful as wastewater processing material.
This document further describes that basic magnesium sulfate is employable for removing silica and lead by adsorption.
JP-A-2003-47972 discloses a method for removing fluorine from wastewater discharged from desulfurization apparatuses which comprises placing magnesium hydroxide as a desulfurising agent in the desulfurization apparatus and adding sodium hydroxide to the wastewater discharged from the apparatus, whereby producing basic magnesium sulfate having adsorbed fluorine and magnesium hydroxide.
As is described above, the granules comprising fibrous basic magnesium sulfate particles can aggregate fine particles and oil contained in wastewater and remove heavy metals and fluorine by adsorption, and hence are valuable as wastewater-processing material.
The basic magnesium sulfate granules to be used as wastewater-processing material preferably have spaces inside of the granule so that water can easily enter the spaces, that means to have a low bulk density, and preferably well maintain their form in running water so that the fibrous particles are well kept in the granules when the granules are placed in running water, that means to have a high strength.
The present inventors have noted that the known basic magnesium sulfate granules do not have a strength enough for employing as wastewater-processing material and that basic magnesium sulfate granules having an increased strength are required.